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CHAPTER - 1

INTRODUCTION

1.1 Hardfacing - Introduction

1.2 Hardfacing - Advantages

1.3 Hardfacing - Uses

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INTRODUCTION

1.1 HARDFACING - INTRODUCTION

“Hardfacing” or “Hardsurfacing”, is the application of depositing specialized

alloys by means of a welding process to resist wear due to abrasion, impact,

corrosion, high temperature etc. These alloys can be deposited on the component

surface, especially at the areas which are subjected to wear through different welding

processes such as Arc Welding, Oxy-Acetylene Welding (commonly called Gas

Welding), TIG Welding etc. In a hard-faced part, the base material is selected to

impart strength and economy, and the hard-facing material is selected for the specific

wearing conditions to which the areas of the part will be subjected in service.

Hardfacing can also be applied to a new component during its manufacture, or it can

be used to re-establish a worn out surface [1]. Welding deposits can help to regain the

components by enhancing their service life [2]. Welding plays a major role in

fulfilling such requirements and also to efficiently deposit hardfacing alloys [3, 4].

Hard-facing extends the life of parts used in machinery or equipment very

efficiently [3, 4]. Hardsurfacing of engineering components by welding processes is

widely adopted among different surface treatment techniques available, as they

require less time, help in effective deposition of extra material only in the worn out

area, impart better strength and wear properties, equipment portability, cost

effectiveness etc. Weld hard facing techniques are mainly used to improve the service

life of engineering parts either by rebuilding in such a way that it produces a

metallic/alloy wall section to resist wear, corrosion, etc. Hard surfacing products are

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used in industries to reduce cost, extend equipment service life, reduce machine

downtime, reduce spare parts inventories etc.

Hard-facing can increase the service life of a component even more than ten times

[5]. In some cases, the cost of hard-facing may appear very expensive due to the cost

of hardfacing alloys used, but, if the costs involved in regular breakdowns to replace

worn out parts are also considered then cost is not only compensated but also is less

[5]. For instance, during Second World War, Gasoline engines were operated 24

hours a day to supply power to mobile oxygen plants. The unhardfaced exhaust valves

gave a life of 7 days where as the hard-faced valves gave a life of 14 days. The cost of

hard-faced valves was very high compared to unhardfaced valves. But replacing the

valves resulted in loss of oxygen production up to eight hours. Hard-faced valves are

definitely economical in such case. Due to result of such considerable savings in

machine down time and production costs this process has been adopted across many

industries [5]. Numerous electrodes for weld Hardfacing have been developed during

recent times [6]. Hardfacing also enhances the wear resistance [7, 8, 9], improves

even the ballistic capabilities [10], reduces wear in ploughshare [11, 12] etc.

Carbon Steels are widely used for producing enormous quantities of components /

parts of the machinery and equipments used in various industries such as Sugar Mills,

Earth Moving, Agriculture, Cement, Dredging, Construction, Rock Quarry / Mining,

Oil Drilling Service, Power Generation / Utilities, etc. These components / parts are

often subjected to wear and tear, cost of operation and maintenance, breakage leading

to increased down times for repair / replacement, wastage of money, material,

manpower, machine utilization etc.

Carbon steels are available in different rolled forms, and also in normalised or

hardened and tempered conditions, with the best properties developed by proper heat

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treatment. Carbon is the main alloying constituent in Carbon steels. As the carbon

content increases, the hardness and strength of the metal increases, but on the other

hand it becomes less ductile and more difficult to weld. The table below enumerates

some of the properties and applications of certain carbon steels.

TABLE: 1.1 PROPERTIES OF CARBON STEELS

Carbon Steel type Percentage of Carbon

Properties Applications

Low carbon steels

< 0.25% Good formability, weldability, low cost, low strength

Machine parts, deep drawing parts, chain, pipe, wire, nails,

Medium carbon steels

0.25 to 0.55%

Good toughness, ductility, relatively good strength

Machine parts, rolls, axles, screws, cylinders, crankshafts,

High carbon steels

> 0.55% High strength, hardness, wear resistance, moderate ductility

Rolling mills, rope wire, screw drivers, hammers, band saws

Tool steels– sub group of high carbon steels

> 0.8% Very high strength, wear resistance, hardness, poor weldability, low ductility

Punches, shear blades, springs, milling cutters, knives, razors

Hence to improve the strength, wear characteristics, life etc these components /

parts are subjected to various treatments such as:

Organic and inorganic coatings like paints, laminates, cements, floor toppings,

hot dippings, autocatalytic platings, furnace fusings, hardfacings, thermal

sprayings, electroplatings etc.

Heat treatments done by flame heating, induction heating etc to improve

hardnesss.

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High energy treatments like laser glazing, ion implantation, and electron beam

treatment.

Diffusion processes like boronizing, Ferritic-nitrocarb, carburizing, nitriding,

carbonitriding etc.

Special treatments, like magnetic, sonic, cryo treatments, which not only affect

the surfaces but also the bulk materials.

1.2 HARDFACING - ADVANTAGES

Hard surfacing products are widely used in engineering applications due to:

1. Reduced costs (25-75% of the cost of a replacement part).

2. Prolonged equipment life (30-300 times, depending upon application).

3. Reduced downtimes since the parts give more life and hence the number of

shutdowns required to replace the parts are less.

4. Reduced inventory of spare parts since worn parts can be rebuilt.

Steel mill roll rebuilt Worn rail end rebuilt Bucket lip hard surfaced

PLATE: 1.1 EXAMPLES OF HARDFACED PARTS

1.3 HARDFACING - USES

The two basic areas where hard surfacing is used are:

1.3.1. To Retrieve Worn out Components

A total solution to metal wear never exists. Hence when components reach their

limits of useful life, two options are possible - to replace the part or to retrieve the life.

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To replace the part it should be available in stock or a new one has to be purchased.

Expensive parts that require frequent replacement must always be kept in the stock.

This increases the inventory costs and also increases administrative expenditure of the

firm, apart from the actual cost of replacement.

Sometimes due to the unavailability of components, longer delays may take place

thus increasing the downtime of equipment and also incur further loss of production

time. On the other hand retrieving the part by Hardfacing techniques can be done at a

lesser cost than that of replacement by a new part. This reduces the loss due to

shortage of spares which further reduce inventory costs and administration costs there

by eliminating the waiting time for replacement of components.

Parts retrieved by hardfacing are often better than new parts. Hardfaced

components give longer life than those that are not hardfaced. Also retrieving the life

by hardfacing in many cases can be done on site itself without the need for complete

or even partial dismantling of the machine. Hardfacing worn out components can save

lot of maintenance expenditure.

1.3.2 To Protect new parts from loss of metal

Hard surfacing can be used on new part also on the areas where it is most subjected

to wear. Depositing a high alloy element offers much better wear resistance than that

of the original base material. Such deposition also increases the working life of the

part up to two or more times than that of a part which is not hard surfaced. The extra

expense involved in Hardfacing can be compensated by using less expensive base

material.

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BIBLIOGRAPHY

[1] E.N. Gregory, “Hardfacing”, Tribology International, 1978, pages 129-134.

[2] Agustín Gualco, Hernán G. Svoboda, Estela S. Surian and Luis A. de Vedia,

“Effect of welding procedure on wear behaviour of a modified martensitic tool

steel hardfacing deposit”, Materials & Design, 2010, Volume 31, Issue 9, 2010,

pages 4165–4173

[3] M. Kirchgaßner, E. Badisch, F. Franek, “Behaviour of iron-based hardfacing

alloys under abrasion and impact”, Wear, Volume 265, Issues 5-6, 2008, pages

772-779.

[4] E. Badisch, M. Kirchgaßner, “Influence of welding parameters on

microstructure and wear behaviour of a typical Ni Cr B Si hardfacing alloy

reinforced with tungsten carbide”, Surface and Coatings Technology, Volume

202, Issue 24, 2008, pages 6016-6022.

[5] http://www.esabna.com/euweb/oxy_handbook/589oxy18_6.htm.

[6] Ashis Kapoor, Teresa Melfi, Damian Kotecki, “Hardfacing Electrode”, United

states Patent Application Publication, Pub. No. US2006/0165552 A1, Pub.Date:

Jul.27, 2006.

[7] Howard S. Avery, “The Measurement of Wear Resistance”, Wear, Volume 4,

1961, pages 427-449.

[8] Kwon-Yeong Lee, Gyung Guk Kim, Ji Hui Kim, Sung-Hoon Lee and Seon-Jin

Kim, “Sliding wear behavior of hardfacing alloys in a pressurized water

environment”, Wear, Volume 262, Issues 7-8, 2007, pages 845-849.

[9] H. Sert, A. Can, H. Arıkan, B. Selcuk, H. Toprak, “Wear behavior of different

surface treated cam spindles”, Wear, Volume 260, 2006, pages 1013-1019.

[10] G. Madhusudhan Reddy, T. Mohandas, K. Papukutty, “Enhancement of ballistic

capabilities of soft welds through hardfacing”, International Journal of Impact

Engineering, Volume 22, Issue 8, 1999, pages 775-791.

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[11] Z. Horvat, D. Filipovic, S. Kosutic and R. Emert, “Reduction of mouldboard

plough share wear by a combination technique of hardfacing” Tribology

International, Volume 41, Issue 8 2008, pages 778-782.

[12] Yilmaz Bayhan, “Reduction of wear via hardfacing of chisel ploughshare”,

Tribology International, Volume 39, Issue 6, 2006, pages 570-574.